1. Field of the Invention
The present invention relates to a printer and a restoration method for a printing plate, utilized mainly in electrophotographic processes using a liquid toner.
2. Description of the Related Art
As a general printing technique, recently digitization of printing processes is progressing. There is thus a challenge to convert an image or the like into digital data by preparing an image or a script with a personal computer or reading an image by a scanner or the like, and to directly utilize the digital data for preparation of a plate used for printing. In this way, a labor-saving effect can be attained in the overall printing processes as well as making highly detailed printing possible.
As a conventional plate, a so-called PS plate is generally known. This plate has a hydrophilic non-image area made of an anodized aluminum oxide, and a hydrophobic image area formed by curing a photosensitive resin on a surface of the non-image area. Printing is performed by transferring ink attached to the hydrophobic image area onto a paper surface. This PS plate is not one which can cope with above mentioned digitization of the printing processes.
On the other hand, in addition to the above described PS plate there has been proposed another method which can cope with digitization of printing processes and make preparation of the plate easy. For example, there is known a method in which a picture line is registered by a laser beam on a PET film on which a laser absorbing layer such as carbon black has been applied and a silicon resin layer has further been applied thereon, to thereby heat the laser absorbing layer so that the silicon resin layer is burnt by the heat to thereby prepare a plate. Moreover, there is known another method in which an lipophilic laser absorbing layer is applied onto an aluminum plate, and a hydrophilic layer is applied thereon, which is then burnt by a laser beam in the same manner as described above to thereby prepare a plate.
With the related art however, there are problems as described below. First, with the PS plate, significant time and cost are required in the preparation thereof so that particularly with the printing of a small number of copies, this causes a cost increase in printing. Moreover, when the printing of one pattern has been completed and the next printing is to be performed, the plate must be replaced, and the formerly used plate discarded. Furthermore, as described above, the PS plate is not one which can cope with the digitization of printing processes. That is to say, with the PS plate, a plate cannot be directly prepared from digital data, making it impossible to realize digitization of printing processes for attaining laborsaving and highly detailed printing.
Moreover, preparation of a plate which can cope with the above described digitization, that is one using a PET film or an aluminum plate can certainly be prepared directly from digital data, but once the printing of one pattern is completed, the plate must be replaced by a new plate for printing to be possible. That means there is no difference to the above described PS plate, in terms of the circumstances that the plate once used must be discarded. That is to say, the printing cost relating to replacement of the plate increases. Furthermore, from the standpoint of global environmental protection which has recently been advocated, discarding a plate used only once is undesirable.
With an electronic editing system using digital data, then as a method for preparing a printing plate directly from the output of a terminal plotter, there is known a method in which after a toner image has been formed on a photosensitive material surface in an electrophotographic process, a non-image area is made hydrophilic using a desensitizer to thereby prepare a printing plate. Moreover, there is another method in which after a toner image has been formed, a photoconductive layer in a non-image area is removed to thereby prepare a printing plate. However, with these plate making methods using the electrophotographic process, restoration of the printing plate for repeated use as with the abovementioned PS plate, the PET film plate, the aluminum plate and the like, has not at all been considered, and a plate used once is discarded.